Chapter 14 Alcohols, Phenols, Ethers, and Thiols 14.5 Physical Properties of Alcohols, Phenols, and Ethers 14.6 Reactions of Alcohols

Boiling Points of Alcohols Alcohols contain a strongly electronegative O in the OH groups. Thus, hydrogen bonds form between alcohol molecules. Hydrogen bonds contribute to higher boiling points for alcohols compared to alkanes and ethers of similar mass.

Boiling Points of Ethers Ethers have an O atom, but there is no H attached. Thus, hydrogen bonds cannot form between ether molecules.

Solubility of Alcohols and Ethers in Water Alcohols and ethers are more soluble in water than alkanes because the oxygen atom can hydrogen bond with water. Alcohols with 1-4 C atoms are soluble, but alcohols with 5 or more C atoms are not.

Reactions of Alcohols Alcohols undergo combustion with O2 to produce CO2 and H2O. 2CH3OH + 3O2 2CO2 + 4H2O + Heat Dehydration removes H- and -OH from adjacent carbon atoms by heating with an acid catalyst. H OH | | H+, heat H—C—C—H H—C=C—H + H2O | | | | H H H H alcohol alkene

Formation of Ethers Ethers form when dehydration takes place at low temperature. H+ CH3—OH + HO—CH3 CH3—O—CH3 + H2O Two Methanol Dimethyl ether

Oxidation and Reduction In organic chemistry, oxidation is a loss of hydrogen atoms or a gain of oxygen. In an oxidation, there is an increase in the number of C-O bonds. Reduction is a gain of hydrogen or a loss of oxygen. The number of C-O bonds decreases.

Oxidation of Primary Alcohols In the oxidation [O] of a primary alcohol, one H is lost from the –OH and another H from the carbon bonded to the OH. [O] Primary alcohol Aldehyde OH O | [O] || CH3—C—H CH3—C—H + H2O | H Ethanol Ethanal (ethyl alcohol) (acetaldehyde)

Oxidation of Secondary Alcohols The oxidation of a secondary alcohol removes one H from –OH and another H from the carbon bonded to the –OH. [O] Secondary alcohol Ketone OH O | [O] || CH3—C—CH3 CH3—C—CH3 + H2O | H 2-Propanol Propanone (Isopropyl alcohol) (Dimethylketone; Acetone)

Oxidation of Tertiary Alcohols Tertiary alcohols are resistant to oxidation. [O] Tertiary alcohols no reaction OH | [O] CH3—C—CH3 no product | CH3 no H on the C-OH to oxidize 2-Methyl-2-propanol

Ethanol CH3CH2OH Ethanol: Acts as a depressant. Kills or disables more people than any other drug. Is metabolized at a rate of 12-15 mg/dL per hour by a social drinker. Is metabolized at a rate of 30 mg/dL per hour by an alcoholic.

Oxidation of Alcohol in the Body Enzymes in the liver oxidize ethanol. The aldehyde produced impairs coordination. A blood alcohol level over 0.4% can be fatal. O || CH3CH2OH CH3CH 2CO2 + H2O Ethyl alcohol acetaldehyde

Oxidation of alcohols in liver

Effect of Alcohol on the Body

Breathalyzer test K2Cr2O7 (potassium dichromate) This orange colored solution is used in the Breathalyzer test (test for blood alcohol level) Potassium dichromate changes color when it is reduced by alcohol K2Cr2O7 oxidizes the alcohol

Breathalyzer reaction orange-red green 8H++Cr2O72-+3C2H5OH→2Cr3++3C2H4O+7H2O dichromate ethyl chromium (III) acetaldehyde ion alcohol ion (from K2Cr2O7)

Alcohol Contents in Common Products % Ethanol Product 50% Whiskey, rum, brandy 40% Flavoring extracts 15-25% Listerine, Nyquil, Scope 12% Wine, Dristan, Cepacol 3-9% Beer, Lavoris

The proof of an alcohol The proof of an alcoholic beverage is merely twice the percentage of alcohol by volume. The term has its origin in an old seventeenth-century English method for testing whiskey. Dealers were often tempted to increase profits by adding water to booze. A qualitative method for testing the whiskey was to pour some of it on gunpowder and ignite it. If the gunpowder ignited after the alcohol had burned away, this was considered “proof” that the whiskey did not contain too much water.

Production of ethanol from grain by fermentation Grain seeds are grounded and cooked → mash Malt (the dried sprouts of barley) or special mold is added → source of the enzyme diastase that catalyzes the conversion of starch to malt sugar, maltose diastase (C6H10O5)2x + H2O → x C12H22O11 starch maltose Pure yeast culture is added C12H22O11 + H2O → 2 C6H12O6 maltose glucose C6H12O6 → 2 CH3CH2OH + 2 CO2 glucose ethanol carbon dioxide

Preparation of alcohols Ethanol is made by hydration of ethylene (ethene) in the presence of acid catalyst

Isopropyl is produced by addition of water to propylene (1-propene)

Methanol is made commercially from carbon monoxide and hydrogen CO + 2H2 → CH3OH

Oxidation of Thiols. Mild oxidizing agens remove two hydrogen atoms from two thiol molecules. The remaining pieces of thiols combine to form a new molecule, disulfide, with a covalent bond between two sulfur atoms. R – S – H H – S – R+I2 → RS – SR+2HI 2 RSH + H2O2 → RS – SR + 2 H2O

The chemistry of the “permanent” waving of hair. Hair is protein, and it is held in shape by disulfide linkages between adjacent protein chains. The first step involves the use of lotion containing a reducing agent such as thioglycolic acid, HS – CH2 – COOH. The wave lotion ruptures the disulfide linkages of the hair protein. The hair is then set on curles or rollers and is treated with a mild oxidizing agent such as hydrogen peroxide (H2O2). Disulfide linkages are formed in new positions to give new shape to the hair. Exactly the same chemical process can be used to straighten naturally curly hair. The change in hair style depends only on how one arranges the hair after the disulfide bonds have been reduced and before the reoxidation takes place. Permanent Hair Wave (http://www.elmhurst.edu/~chm/vchembook/568hairwave.html)